The present invention relates to an improvement of the refrigerant compressor, more particularly, to a compressor automatically adjustable in the suction efficiency of the refrigerant gas by means of varying the flow passage area of the suction port of the refrigerant gas to the compressing chamber, in response to the load variation of the refrigerating system.
In a refrigerating system, an expansion valve is generally installed between a condensor and an evaporator, which is adjusted in the degree of opening according to the load variation, for controlling the flow amount of the refrigerant. When the load is decreased and the expansion valve is choked excessively, however, the inner pressure in the evaporator is liable to be lowered too much, which excessively lowers the temperature in the evaporator to induce freezing on the outer wall of the evaporator, resulting in obstructing the flow of the air-to-be-cooled. In order to prevent this undesirable phenomenon, attempts have been conventionally made, one being (1) a method of releasing the clutch disposed between the compressor and the driving source, when the temperature of the air which passes the evaporator has come down to a certain value; and another being (2) a method of disposing an evaporating-pressure-adjusting-valve at the outlet port of the evaporator for preventing the pressure descending in the evaporator below a certain value. The former is defective in the short life of the clutch due to too high frequency of "on-off" operation of the same, and a rapid increase of load to the driving source at every clutch connection. Especially when the refrigerant compressor is in use for vehicle airconditioning, the engine load of the vehicle is rapidly increased to cause a disagreeable drive-feeling. The latter, which is not affected by the on-off of the clutch, is also unsatisfactory in the positioning of the evaporating-pressure-adjusting-valve at the outlet port of the evaporator. When the valve is choked, because of a low load, in the piping from the valve to the compressor as well as in the suction chamber and other vacant chambers in the compressor, the refrigerant pressure from there to the compressor will come down to an extremely low level, which lowers the temperature of the refrigerant to increase the temperature difference against the piping and compressor (a refrigerant which shows the temperature 5.degree.-10.degree. C. at the pressure 2 atg. will be lowered in temperature to -15.degree.--20.degree. C. as the pressure descends down to 0.5 atg.). The greater the temperature difference becomes, the more useless heat absorption takes place by the refrigerant from the atmosphere around the piping; in addition, the heat which ought to be dispersed into the atmosphere from the compressor will be unfavorably absorbed by the refrigerant. This not only reduces the efficiency of the refrigerating cycle, but also brings about a rising of the super-heat of the refrigerant (temperature rising exceeding the saturation temperature), which is liable to result in a seizure of the compressor. When the refrigerant, which is already heated to a super-heat having absorbed a large amount of heat before being sucked into the compressing chamber, is compressed in the compressor, its temperature becomes higher than usual.
A refrigerant showing 5.degree. C. at the pressure 1.5 atg. just before the suction valve of the compressor will be, when compressed in the compressor up to 15 atg., heated to 80.degree. C., while a refrigerant showing 0.degree. C., having absorbed a relatively large heat amount, under the pressure of 0.5 atg. will be, when compressed up to 15 atg., heated up to about 90.degree. C. The temperature rise in the discharged gas will, via the blow-by gas, heat excessively each sliding portion, and is liable to result in a seizure of the compressor. The temperature, rise, furthermore, causes the excessive heat of the compressing chamber and its vicinities as well as discharging chamber, while the suction side, such as a passage, a suction chamber, and its environments, is maintained in low temperature cooled by the refrigerant which is colder than usual. This will cause a great temperature difference between the suction side and the discharge side, which is likely to cause a strain or deformation in the compressor, especially in an aluminum compressor used for weight reduction.